Pasteurized Dairy Foods Free of Live Bird Flu, Federal Tests Confirm

But the scope of the outbreak among cattle remains uncertain, and little human testing has been done.

Additional testing of retail dairy products from across the country has turned up no signs of live bird flu virus, strengthening the consensus that pasteurization is protecting consumers from the threat, federal health and agriculture officials said at a news briefing on Wednesday.

But the scope of the bird flu outbreak in cattle remains unclear, as dairy herds are not routinely tested for the infection, scientists and other experts have noted.

Just one human infection, which was mild, has been reported, in a dairy worker in Texas who had direct contact with sick cows. But scientists fear there may be many more undetected infections, particularly among farm workers.

Barely two dozen people have been tested for bird flu, federal officials said at the briefing. There have been no unusual increases in flu cases around the country, even in areas with infected cows, they added.

But Dr. Keith Poulsen, director of the Wisconsin Veterinary Diagnostic Laboratory, said that farms are not required to test employees, many of whom are migrant workers who are reluctant to work with state health officials.

“How much are we ignoring because of anxiety and fear of what happens if you don’t get an answer that you like?” Dr. Poulsen said.